The invention relates to a novel hydrocarbon base oil for high end lubricants, obtained from hydrocarbon cuts of various provenances. More precisely, the invention relates to an oil of this type, with a viscosity index VI, calculated according to the French standard NF T 60-136, greater than 130, for a kinematic viscosity measured at 100xc2x0 C. (Vk@100xc2x0 C.), measured according to the NF standard T 60-100, ranging between 3.5 and 4.5 mm2/s (or cSt). This novel base oil has a preferred application in the formulations of lubricants for engines, in particular in the automobile industry, as well as for industrial use.
The base oils are currently classed in five groups according to the API classification, based on characteristics defined in Table I hereafter:
For a long time, Group 1 base oils for lubricants have been produced from certain distillate cuts obtained through distillation under vacuum of paraffin base crude oils since it is the high isoparaffin content of said crude oils that gives them good VI values. These distillates undergo a solvent extraction, resulting in a raffinate rich in paraffins and an extract rich in aromatics; the raffinate is then dewaxed by mixing it with an organic solvent (for example, methyl ethyl ketone or MEK), it is cooled and filtrated in order to obtain, through separation, solid paraffins or slack wax (elimination of the n-paraffins) and an oil with a VI of at least 95 and good properties when cold (pour point); lastly this oil undergoes a hydrofinishing to stabilize it and improve its color.
We remind you that the calculation of the viscosity index or VI of the oil products is done from their kinematic viscosities at 40xc2x0 C. and at 100xc2x0 C., according to the NF standard T 60-136.
However, for several years, stricter and stricter operating conditions for automobile engines have lead to more limiting specifications for base oils from which are formulated the engine oils, in particular a decrease in their volatility and a lower pour point and an increase of their VI (above 105). Yet such characteristics cannot be obtained solely by means of a solvent extraction of the distillation cuts (xe2x80x9cstraight runxe2x80x9d), hence the development of oil production processes from other cuts, such as those resulting from catalytic hydrocracking and/or catalytic hydrodewaxing. Indeed, the saturation of the aromatic compounds and the decyclization of the naphthenes mainly take place during the hydrocracking reaction of the hydrocarbon charges, whereas the hydrodewaxing reaction causes the cracking and isomerization of the n-paraffins and improves the cold properties of the lubricating bases obtained.
Such bases, obtained from hydrocracking residues subjected to a solvent dewaxing, and belonging to group III according to the above-described API classification, are currently generated, in particular by the applicant, under the name NHC5 (xe2x80x9cNeutral HydroCrackedxe2x80x9d) with a Vk@100xc2x0 C. of 4.5 to 5 mm2/s (4.5 to 5 cSt).
The man of the art already knows he can produce lubricant base oils with a high viscosity index (VI), for example greater than 125, from hydrocarbon charges originating from the heavy cuts or residues of a hydrocracker. The French patent application 2 194 767 A describes, in particular a method for preparing a lubricant oil with a high VI, comprising a catalytic hydrocracking treatment of a mineral oil cut with a high boiling point, a fractionation of the effluents, a dewaxing of the boiling residue above 350xc2x0 C. and a catalytic hydroisomerization of the paraffin obtained.
The association of hydrocracking and isomerization phases with specific catalysts, for the manufacture of lubricants with a high VI is also described in EP 0 574 191 A and EP 0 597 935 A. This is also the case in EP 0 744 452 A that describes a method for producing such base oils, including a hydrocracking phase with a platinum and/or palladium base catalyst of a hydrocracking bottom cut so as to convert at least 25% by weight of the hydrocarbon cut with a boiling point of at least 370xc2x0 C., followed by an effluent fractionation phase, where the heavy cut has a VI of at least 125 and preferably greater than 135, with a kinematic viscosity at 100xc2x0 C. of at least 3.5 mm2/s or cSt, where the heavy cut is then subjected to a dewaxing phase. However, these patents or published applications do not give any details as to the cold properties of the lubricant bases obtained, such as their pour point, or their structure.
Another known way to obtain base oils with a high VI is from very high paraffin-base hydrocarbon charges, in particular consisting of n-paraffin or wax compounds obtained via Fischer-Tropsch synthesis or of slack wax. This is how EP 0 323 092 A describes a method for producing oil with a high VI, comprising hydrotreatment, catalytic hydroisomerization and dewaxing phases, and WO 97/21788 A describes a method for producing a biodegradable lubricating base oil that includes hydroisomerization and catalytic hydrocracking of a cut with a boiling point that is greater than 370xc2x0 C. of a Fischer-Tropsch paraffin charge, fractionation of the effluent obtained, whose heavy cut contains paraffins branched by methyl radicals, and lastly solvent dewaxing. Although this last application describes a rate of ramification per molecule that ranges between 6 and 7.5 methyl groups for 100 carbon atoms, it is stated that there are very few ramifications by groups with 2 or more carbon atoms (ethyl).
Yet surprisingly, the applicant has established that the quality of these oils is linked to the isoparaffinic nature of the hydrocarbon chains of the cuts used and, in particular, has a specific relation between the different types of substitutes carried by said chains.
Therefore, the object of this invention is to obtain a novel base oil for high end lubricants, obtained from hydrocarbon cuts of various provenances, with a high viscosity index and improved cold properties, in particular a pour point of less than xe2x88x9218xc2x0 C., guaranteeing theological properties that are satisfactory for the finished lubricating oils formulated from this base oil, in a wide range of temperatures (from xe2x88x9230 to +100xc2x0 C.), thanks to a specific ramification structure of the paraffin base molecules of which it consists.
We noted in particular that the base oil as set forth in the invention has a much better performance than the bases currently available on the market, resulting from hydrocracked products and having undergone a solvent dewaxing (NHC5 type oils), or a catalytic dewaxing, and that belong to group III based on the API classification described above. Surprisingly, it can also replace known synthetic bases such as the poly-alpha olefins (PAO), that belong to group IV, whose performances are well known for increasing the VI, but that have the major disadvantage of costing much more than the bases of mineral origin.
With this in mind, the object of the invention is a novel hydrocarbon base oil for lubricants, with a viscosity index or VI greater than or equal to 130, comprising mainly long, isoparaffin base, hydrocarbon chains, branched over several carbon atoms, characterized in that said chains comprise a number of carbon atoms greater than 25 and have a ratio of the number of substitutes consisting of at least two carbon atoms over the number of methyl type substitutes, greater than or equal to 0.9.
Indeed, it has been established that when the value of this ratio, for a base oil, is less than 0.9, the characteristics of the finished lubricating oils obtained from this base don""t perform as well.
Preferably, said hydrocarbon chains have a ratio of the number of substitutes comprised of at least two carbon atoms, over the number of long chain CH2, expressed in %, greater than or equal to 23%.
In particular, the base oil as set forth in the invention has a ratio of the viscosity index when cold (VIF) over the viscosity index (VI) (measured according to the NF standard T 60-136) greater than or equal to 1.
Advantageously, the base oil has a naphthenic molecule content that is less than or equal to 10%.
In particular, the base oil has a Noack volatility value of less than 13% by weight (calculated according to the standard CEC-L-40-A 95) as well as a pour point (calculated according to the NF standard T 60-105) of less than xe2x88x9218xc2x0 C. Furthermore, it has a Saybolt color value of +30 (measured according to the ASTM method D 156).
Furthermore, the base oil has a cold viscosity index (VIF) greater than 125.
More particularly, the base oil has a dynamic viscosity CCS at xe2x88x9230xc2x0 C. of less than 1200 mPa.s (calculated according to the ASTM standard D 5293) for a kinematic viscosity Vk at 100xc2x0 C. of 4 mm2/s.
In particular, the base oil as set forth in the invention has a viscosity index VI that is greater than 130 and less than or equal to 135, for a kinematic viscosity Vk at 100xc2x0 C. ranging between 3.5 and 4.5 mm2/s or cSt.
More precisely, this base oil has a viscosity index VI that is greater than 135 for a kinematic viscosity Vk at 100xc2x0 C. that ranges between 4.5 and 5 mm2/s.
A second object of this invention relates to the use of the base oil as defined above, in the formulation of lubricants for engines, in particular for automobiles, namely with the intent to formulate an OW30 grade.
A third object of the invention relates to a method for preparing base oil as set forth in the invention consisting successively of hydrotreatment, hydrodewaxing, fractionation, and hydrofinishing phases of cuts of residues resulting from hydrocracking.